The conventional water scooter is provided with an impeller for drawing and compressing water flow, which is then forced through a nozzle to form jet flow to propel the boat. As shown in FIG. 1, the propelling system of the prior art consists of an engine 12 mounted in the hull 10, a transmission shaft 13 driven by the engine 12 and fastened at the rear end thereof with an impeller 14. The rear end of the transmission shaft 13 is located in a channel 11 of the hull 10. A stator 15 is located in the channel 11 and behind the impeller 14. The stator 15 has an axial portion of a straight cylindrical construction. The axial portion is provided in the periphery thereof with a plurality of stator vanes 151.
In operation, the transmission shaft 13 is driven by the engine 12 to actuate the impeller 14 to rotate rapidly to draw the water into the channel 11 in which the water is compressed. The compressed water is guided into the stator 15. The water flow in the state of vortex is guided by the stator vanes 151 to move forward in a linear direction parallel to the channel 11. The backward thrust of water is generated by the water flow passing the nozzle 16, so as to propel the hull 10.
The size of the gap between the blades 141 of the impeller 14 and the stator vanes 151 of the stator 15 plays an important role in determining the efficiency of the propelling system. The gap of the conventional propelling system described above is so fixed that it can not be adjusted. If the gap is relatively small, the composite flow speed of water flow increases relatively at the time when the power boat is cruising at a high speed. As a result, the entry angle of the water flow becomes greater such that the water flow can not be guided into the stator vanes precisely and efficiently, and that the efficiency of the propelling system is thus seriously undermined. If the gap is relatively large, the composite flow speed of water flow decreases relatively at such time when the power boat is started to cruise or is cruising slowly. As a result, the erosion phenomenon of the power boat is easily brought about.